In this recipe, we will change the cryptographic ciphers that OpenVPN uses. Initially, we will change the cipher only on the client side, which will cause the initialization of the VPN connection to fail. The primary purpose of this recipe is to show the error messages that appear, not to explore the different types of ciphers that OpenVPN supports.
Install OpenVPN 2.0 or higher on two computers. Make sure the computers are connected over a network. Set up the client and server certificates using the first recipe from Chapter 2. For this recipe, the server computer was running CentOS 5 Linux and OpenVPN 2.1.1. The client was running Fedora 13 Linux and OpenVPN 2.1.1. Keep the configuration file basic-udp-server.conf from the Chapter 2 recipe Server-side routing at hand, as well as the client configuration file basic-udp-client.conf.